Understanding the 5 W’s of Post Op Fever and Its Variations

Post-operative fever can occur as the result of a number of different reasons. To help ease the process of determining the causative factor, a special mnemonic was developed that we have come to know as the 5 W’s of post op fever.

What exactly are the 5 W’s? Learn everything you need to know about this classic mnemonic by reading the following guide to the 5 W’s of post-operative fever.

Why a Fever Can Be a Cause for Alarm

What is a fever? A fever is a sign of inflammation, meaning that it most commonly indicates that there is an underlying illness or even a bodily injury. As a result of this, we most often associate fevers with the flu or the cold. However, fevers may be seen with any type of infection (skin infection, pneumonia, etc.) and may also be associated with certain autoimmune diseases. Less commonly, it may be caused by certain medications that one is taking.

It is important to keep in mind, however, that a fever, in and of itself, is not a disease.

A fever appears to be one way your body fights an underlying illness i.e. your body raises its temperature via its internal thermostat (located within a portion of the brain called the hypothalamus) to help your immune system to defeat an infection.

In this context, fevers can occur following surgery for a variety of reasons.  Understanding the causes of fevers in the post-operative period are important as some fevers in the post-operative period can be indicative of a serious complication.

Ideally, an individual should not develop a fever after a surgery. While uncommon, if a fever does develop, then early recognition of the cause of fever is important.

The 5 W’s of post-operative fevers is an easy way to remember the likely causes for pyrexia at specific times after a person undergoes a surgery.

The Traditional Meaning of the 5 W’s

The original 5 W’s are as follows: wind, water, wound, walking, and wonder drug. There are some variations to this which we will discuss later in this article.


The first “W” in the mnemonic represents wind. This pertains to any condition of the lung that causes fever. Typically, fevers that develop within the first 24 to 48 hours after a surgery are related to the lungs. The most common cause of a post-operative fever in this setting, is atelectasis.

There are many kinds of surgery done under general anesthesia. With general anesthesia, you are “put to sleep” and your breathing is slowed down. The breaths you take are not as deep as you normally take when you are up and active. These shallower breaths keep some of the tiny air sacs in your lungs (called alveoli) from fully filling with air. As a result of this, these sacs can flatten. Additionally, following surgery, inactivity, pain, and the side effects of pain medications, can further contribute to this slowed, shallow breathing. Particularly an accumulation of mucus in the airways can lead to localized blockage. This is particularly common after abdominal or chest surgery.

The collapse of these air sacs following surgery is one of the most significant causes of atelectasis, which is a common minor complication seen in patients undergoing general anesthesia. Atelectasis, if more severe, can lead to hypoxia (decreased oxygenation). While it does not always cause fever, while concrete evidence seems to be lacking, it is still common thinking that one of the most common causes of fever post-operatively is atelectasis. Furthermore, if not appropriately addressed, atelectasis can lead to complications like pneumonia or even respiratory failure.

Pneumonia is an infection of the lung that can be caused by bacteria or a virus. After surgery, a lowered immunity is not uncommon. Subsequently, you are at higher risk of developing a pneumonia. Another more common thought is that that if atelectasis is not appropriately addressed with deep breathing post-operatively, that the risk of developing a pneumonia is higher. 


A fever that develops 3 to 5 days after surgery could be indicative of a urinary tract infection – represented by the word water. Foley catheters are oftentimes inserted prior to surgery. This is performed for a variety of reasons including sanitation, as the patient may temporarily lose control of his / her bladder function when they undergo general anesthesia. 

According to the Center of Disease Controls (CDC) statistics, 75% of UTIs acquired in the hospital setting are caused by urinary catheters. That is why, following surgery, most doctors push to have the foley catheter removed as quickly as possible.

Urinary tract infections are mainly caused by bacteria. Therefore, its treatment involves the administration of antibiotics in order to eradicate the infection.

Therefore, if a fever develops anywhere between 3 to 5 days after an operation, the suspicion for a possible urinary tract infection should be high.


When a patient develops a fever 5 to 7 days after a surgery, the causative factor for fever is most likely an infection of the wound, either superficial or deep.

Again, as mentioned previously, one of the ways our body fights infection is by increasing its temperature. This allows the immune system work more efficiently and may actually limit bacterial growth.

When compared to the temperature of the rest of the body, a little bit of warmth of the skin surrounding a post-operative wound is normal. However, if the wound continues to get hotter, is associated with increasing redness, or pustulent drainage, then it’s possible the wound may have become infected. In response to this, the body may raise its temperature as a whole, leading to fever.

It’s vital that healthcare professionals act on this type of fever immediately, as infections of wounds can easily spread causing significant consequences.


The fourth “W” standings for walking. This is meant to represent a deep vein thrombosis — or, in other words, a blood clot. Further, as deep vein thromboses can lead to pulmonary embolisms, it is inclusive of this as well.

A thrombosis is usually a cause for concern because it can have serious implications and may even lead to death. Commonly, these clots collect in deep veins that return blood from the legs towards the heart. After surgery, as patients typically are less likely to be walking, this causes the blood in the legs to be stagnant. This is what increases the risk of a blood clot. Hence, this is why the 5 W’s mnemonic uses the term walking. As it is the lack of walking that significantly increases the risk of a blood clot or deep vein thrombosis (DVT).

While DVTs themselves are not significantly dangerous, some may dislodge and travel to the lungs. This can lead to serious lung and heart issues and even death. This is why the prevention and treatment of DVTs is so important.  Why DVTs cause fever is somewhat controversial, however, it is still common thinking that DVTs are indeed associated with fever. Thus, if a patient develops a fever 5 days or more after a surgery it is important for doctors to consider the possibility of a DVT. This is particularly true in a patient who has not been walking very much.

Wonder Drugs

During a surgery, medications and blood products are administered to keep patients comfortable and healthy. However, sometimes these drugs or blood products might not be fully compatible with a person’s system. The body may reject the substances which may actually lead to the development of a fever on top of a host of other symptoms such as chills, rigor, changes in heart rate, respiratory rate, and blood pressure.

Sometimes these reactions may be life threatening, during which immediate treatment is required by the treating doctor. Other times, the fever and symptoms may resolve within a short period of time without any specific treatment.

A fever of this nature (wonder drugs) can occur anytime during or after a surgery. This is what makes it particularly tricky to pinpoint as a cause of fever, as the time-frame for this particular cause overlaps with all of the other four possible causes of fever.

Variations to the 5 W’s

Some other variations of the 5 W’s have surfaced over the years.

Two other possible causes include – (W)abscess and waterway.

(W)abscess refers to an infection of a soft tissue space or organ. Similar to wound, this usually occurs 5 to 7 days post-op and in this context, is most commonly associated with the wound itself. However, it is important to note that an abscess does not necessarily involve the surgical incision or space, and may thus require a completely different treatment angle.

Waterway refers to a fever caused by an infection of the bloodstream, or septicemia. This type of infection occurs when a bacterial infection somewhere in the body makes its way into the bloodstream. This poses a particular threat as blood travels throughout the entire system, so any bacteria contained in the vessels can easily travel to and infect other parts of the body.

Bloodstream infections can occur anytime after a surgery. So doctors should always keep this in mind when determining the cause of a fever after surgery.

In Closing

The 5 W’s of post-operative fever is a simple mnemonic that can help medical personnel to identify the cause of a fever based on the timeframe within which is occurs.

It is important to keep in mind, however, that this is a basic guideline and should in no way be considered a comprehensive guide to the work-up of a post-operative fever.

Of course, as always note that the information in this article is purely informative and should never be used in place of the advice of your treating physicians.

Dr. Andrew Chung
Dr. Andrew Chung

Dr. Andrew Chung is a Spine Surgeon at Sonoran Spine in Tempe, Arizona. He is a graduate of the Philadelphia College of Osteopathic Medicine and was formerly Spine Surgeon Clinical Fellow at Cedars-Sinai, Spine Surgery Fellow at Keck Hospital, University of Southern California and Chief Resident and an Instructor of Orthopedic Surgery in the Department of Orthopedic Surgery at the Mayo Clinic in Arizona. Dr. Chung's research.